<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>

</body>
<script>
  let a = 30;
  b = '';
  switch (true) {
    case a < 60:
      return b = '123123123';
      // console.log('还需努力')
      // break;
    case a > 60 && a < 80:
      console.log('良好')
      break;
    case a > 80:
      console.log('优秀')
      break;
    default:
      return console.log('踩点大神！')
      break;
  }
  console.log('kkkkk')
</script>

</html>